Express disapproval when trust is often lacking (3)
I believe the answer is:
tut
'express disapproval' is the definition.
(tutting is making a disapproving sound)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tut that I've seen before include "That's bad!" , "former ruler, in brief" , "Exclamation of disapproval or annoyance" , "Sound of mild disapproval" , "Expression of disapproval, usually doubled" .)